Device for matching number of operating bridges on converting substations of direct-current transmission lines

ABSTRACT

A device for matching the number of operating bridges on converting substations of a direct-current transmission line comprising a comparator for comparing the voltage of the transmission pole relative to earth with the voltage of an auxiliary source which depends on the number of the operating bridges of the transmission pole, a unit for disconnecting the bridges connected to the comparator and including actuating elements and elements with various time delays, in which the unit for disconnecting the bridges has a switch for selecting the succession of disconnection of the bridges, the number of positions of the switch corresponding to the number of bridges of the transmission poles while the commutating circuits of the switch being subdivided into groups with the number of circuits in each group being equal to the number of positions of the switch, in which case in each group the commutating circuits on one side are interconnected and are correspondingly connected to the elements with different time delays and on the other side the commutating circuits are connected to the actuating elements of the unit for disconnecting the bridges. The device increases the reliability in controlling a directcurrent transmission line.

United States Patent Gurevich et al.

[ May 30, 1972 Shaposhnikov, Chongarsky bulvar, l3, kv. 53, both of Moscow, all of USSR.

[22] Filed: Jan. 26, 1970 [21] Appl.No.: 5,473

..307/82 ..l-l02j 1/00 .............307/s2,20,52,11,57,43

52 u.s.c1.. 51 Int.Cl..., 58 Field ofSearch [56] References Cited UNITED STATES PATENTS 3,331,990 7/1967 Johansson ..3l7/31 3,526,779 9/ l 970 Uhlmann ..307/20 Primary Examiner-Hennan J. l-lohauser Attorney-Waters, Roditi, Schwartz & Nissen [57] ABSTRACT A device for matching the number of operating bridges on converting substations of a direct-current transmission line comprising a comparator for comparing the voltage of the transmission pole relative to earth with the voltage of an auxiliary source which depends on the number of the operating bridges of the transmission pole, a unit for disconnecting the bridges connected to the comparator and including actuating elements and elements with various time delays, in which the unit for disconnecting the bridges has a switch for selecting the succession of disconnection of the bridges, the number of positions of the switch corresponding to the number of bridges of the transmission poles while the commutating circuits of the switch being subdivided into groups with the number of circuits in each group being equal to the number of positions of the switch, in which case in each group the commutating circuits on one side are interconnected and are correspondingly connected to the elements with different time delays and on the other side the commutating circuits are connected to the actuating elements of the unit for disconnecting the bridges.

The device increases the reliability in controlling a direct-current transmission line.

2 Claims, 1 Drawing Figure Z3 IF I; i l l g 46 47 48 49 I: 27 25m) 221/5)? 32 29/11)? j} I M4 :7 3 l 1 I M t Mitten. I ll l t i 50 H 1' g I? if I j v42 43 44 45 {g4 25 f $4 35 56 $37 Patented May 30, 1972 llllllllllllllll In lllllllllllll II w J 7 mm %W aw mm W w L? g Q %N \N 3 3 Nu n m u n 3 3 S w A A A A x I J gm WI Q0 MN Q Kg: N m a ax n "a m DEVICE FOR MATCHING NUMBER OF OPERATING BRIDGES ON CONVERTING SUBSTATIONS OF DIRECT- CURRENT TRANSMISSION LINFB The present invention relates to high-voltage direct-current transmission lines and, more particularly, the invention relates to devices for matching the number of operating bridges on converting substations of such lines.

These devices are intended for detecting and eliminating abnormal operating conditions in the transmission line which are dangerous for the equipment of the converting bridges. It is known that under normal conditions at two converting substations connected by a direct-current transmission line an equal number of converting bridges are involved which are connected to a given transmission pole. Upon emergency disconnection (shunting) of one or several bridges in one of the substations, the voltage across the pole of the faulty end of the transmission line decreases by a value equal to the voltage of the disconnected bridges. To avoid an excessive rise or, oppositely, decrease of current (upon shunting of the bridges of the inverter or rectifier substations, respectively), the controlling means of the sound end of the transmission pole are capable of considerably, and rapidly enough, increasing the ignition angles of the valves of all the bridges remaining in operation at that end so that the voltage at both ends of the transmission pole is balanced and, as a result, the current of the given pole remains practically the same. The operation at high ignition angles, however, is admissible for only a short time, since it presents danger to the valves and the other equipment of the substation. To prevent this operating mode, the number of operating bridges is then balanced by disconnecting (shunting) extra bridges of the given pole at the sound end of the transmission line so that the ignition angles of the valves return to the normal value and the transmission line continues operation.

The disconnection of bridges at the opposite end of the line and disconnection of extra bridges at the sound end of the line is detected and performed by special means capable of balancing the number of the operating bridges at both ends of the transmission pole. Generally, such means are known as a device for matching the number of operating bridges.

Knownin the art are devices for matching the number of operating bridges employed in direct-current transmission lines. These devices are based on the comparison .of the actual voltage of a transmission pole relative to earth with a reference voltage or current developed by a stabilized directcurrent power source whose circuit is provided with a resistance the value of which depends on the number of operating bridges. Operating bridges are all the converting bridges of the transmission pole of a given converting substation which perform their normal function (i.e., are not shunted by special shunting apparatus). Shunting of one or several bridges of the transmission pole on one of the converting substation is followed by a corresponding voltage drop on the other substation while the reference voltage (current) retains its predetermined value. This results in operation of a comparator unit which through a disconnector switches of the extra bridges, the disconnection of the bridges being effected with difierent time delays rising as fast as the quantity of the bridges being disconnected is increased.

The main disadvantage of the known devices consists in a stringent order of disconnection of the bridges resulting in that each bridge is disconnected with a constant time delay, i.e. this system is not suitable for selecting a bridge from which it is desirable to begin the operation of disconnection. In practice of service the above mentioned absence of selectivity during the operation results in thatthe stably operating bridges are sometimes disconnected first, whereas the unstably operating bridges remain to be switched on.

Besides, in some cases, during the operation with an incomplete number of the bridges the disconnection thereof is carried out with much too long time delays, and this adversely affects the operation032of the rectifiers and other equipment.

An object of the present invention is to eliminate the abovementioned disadvantages.

The main object of the invention is to provide a device for matching the number of operating bridges of converting substations of a direct-current transmission line which would provide for such a succession in disconnecting the bridges that a preselected bridge is primarily switched off, whereas the other bridges are disconnected according to a prescribed program.

Besides, when running a system with an incomplete number of the bridges, such a device makes it possible to reduce the time of disconnection of the other bridges by changing over the time delays of disconnection, corresponding to the shunted bridges, to the next bridges to be switched off after the said shunted bridges according to the prescribed program.

These objects are accomplished by providing a device for matching the number of operating bridges on converting substations of a direct-current transmission line comprising a comparator for comparing the voltage of the transmission pole relative to earth with a voltage of an auxiliary source, depend ing on the number of operating bridges of the transmission pole, and a unit for disconnecting the bridges, which unit is connected to the comparator and is provided with actuating elements and with elements having different rising time delays, according to the invention, the unit for disconnecting the bridges is also provided with a switch for selecting such a succession of disconnection of the bridges that a preselected bridge is disconnected first, whereas the other bridges are disconnected according to a prescribed program, for which purpose the number of positions of the switch corresponds to the number of bridges of the transmission pole in each substation while the commutating circuits of the switch are subdivided into groups, in each of which the number of such circuits is equal to the number of the switch positions, in which case the commutating circuits of each group on one side are interconnected and are correspondingly connected to the elements with difierent time delays whileon the gther side they are connected to the actuating elements for disconnecting the bridges.

Besides, it is expedient that between the commutating circuits of the switch at the side of connection of these circuits with the actuating elements of the unit for disconnecting the bridges there are inserted commutating elements, each of which closes the circuitwhen a corresponding shunting apparatus is on, thus preparing for subsequent operation of the device the transfer of the time delays of disconnection, corresponding to the shunted bridges, to the next bridges to be disconnected subsequent to the shunted bridges by the prescribed program.

The device for matching the number of operating bridges on converting substations of a direct-current transmission line made according to the present invention enables the problem in hand to be successively solved. It takes it possible to improve the flexibility in controlling the transmission by means of selecting a bridge to be disconnected first during the opera tion of the device and this fact, on taking into account the working capacity of the bridges, allows the number of operating bridges to be as high as possible.

The device also makes it possible to reduce the time required for balancing the quantity of bridges at the ends of the transmission line and this helps to decrease the period of an abnormal operation of this line, which fact, in turn, considerably decreases the probability of damaging the valves and other equipment and increases the reliability of the transmission line in operation.

For a better understanding of the invention, given below is a detailed description of the invention in the form of a device for matching the number of operating bridges for one pole of a converting substation which comprises four rectifier bridges,

reference being made to the accompanying drawing illustratof the device considered herein, the comparator consists of a double-wound polarized relay 1 whose bucking winding 2 is connected to a low-voltage capacitance-resistance measuring voltage divider 3 through a rectifier 4. The working winding 5 through a contact 6 of a current relay 7 inserted into the secondary circuit of the measuring transformer 8 of the transmission line, is connected to the circuit of the stabilized d-c source 9 through a resistor 10, the resistance of which is varied by bringing or debridging the portions of this resistor 10 through contacts 11,13 of special relays (the relay windings are not shown), controlling the number of rectifier bridges 18-21 closed by shunting apparatus 14-17. These relays serve to alter the actuation setting of the device for different numbers of operating bridges (which are not shunted by the apparatus 14-17). Each of the three relays operates for a specific number of bridges shunted by the apparatus 14-17, which is achieved by very simple logical combinations of the blocking contacts of these apparatus. Thus, the lower. the operating voltage of the transmission pole, i.e., the greater the number of shunted bridges, the more relays operate and the more contacts 1113 are open, the greater the magnitude of the resistor 10in the circuit of the source 9 and, accordingly, the lower the level of the voltage setting required to actuate the device. Inserted through the contact 22 of the relay 1 of the comparator is a unit for disconnecting the bridges comprising time elements in the considered embodiment of the invention are made in the form of electromechanical time relays 24 and 25. The time relay 24 is provided with a sliding contact26 and a contact 27, while the time relay 25 is provided with two sliding contacts 28 and 29. The employment of delay elements in the device circuit, with the bridges of the sound end of the transmission pole being disconnected in succession in accordance with the delay time of the delay elements, is dictated by the necessity to prevent the actuation of the device during shortduration disturbances followed by temporary voltage drops. By means of a sliding contact 26 of the relay 24, a time delay n is set for switching off the bridge which is to be disconnected first, the second contact 27 of this relay being used for triggering the time relay 25. Sliding contacts 28 and 29 are used for setting time delays t and 1 to disconnect the second and third bridges respectively, according to a prescribed program. The contacts 26, 28 and 29 of the time relays 24, 25 are connected to a switch 30 for selecting the order of disconnection of the bridges, said switch having positions I-IV according to the number of bridges of thetransmission pole. The contacts or: the switch 30 are subdivided into groups 31-33, each group including the contacts I-IV which are respectively closed in each position of the switch.

In each group 31-33 the contacts on one side are combined and correspondingly connected to the contacts 26, 28, 29 of the time relays 24, 25. On the other side each contacts of the group 31 is connected to one of the actuating element of the unit for disconnecting the bridges, which in the considered version of the device consists of electromechanical relays 34-37 inserted through normally closed contacts 38-41 of repeating relays 42-45 following the position of the blocking contacts 46-49 of the shunting apparatus 14-17 of the bridges 18-21. W N

The contacts l-IV of the groups 32 and 33 of the switch 30 can be connected to the relays 34-37 in various ways depending on the prescribed program of disconnection of the bridges. In the version of the device considered herein the contact 1 of the group 32 is connected to the relay 35, the contacts lI-IV of the same group are connected to the relay 34, the contacts I,II of the group 33 are connected to the delay 36 and the contacts III,IV of the same group are connected to the relay 3 7. v

Inserted between the circuits of the switch 30 on the side of connection of the actuating relays 34-37 are commutating elements consisting of normally open contacts 50 55 of the corresponding relays 42-45 following the position of the blocking contacts 46-49.

serted between the contacts I and II, the contact 51 of the relay 43 is inserted between the contacts II and III, the contact 52 of the relay 44 is inserted between the contacts I and III, the contact 53 of the relay 45 is inserted between the contacts I and IV of the group 31 of the switch 30.

The device operates in the following way.

On switching on the transmission pole, the device is put into operation through the contact 6 of the current relay 7 inserted into the secondary circuit of the direct-current measuring transformer 8 of the transmission line.

In normal operating conditions, when the numbers of bridges on the transmission substations are equal, the relay 1 does not operate as the current through the bucking windin g 2 of the relay 1 determined by the voltage of the low-tension arm of the divider 3 somewhat exceeds the current through the working winding 5 determined by the voltage of the auxiliary source 9 and by the value of the resistor 10 (completely or partially introduced into its circuit by the contacts 1 1-13 of the relay for counting the quantity of the operating bridges).

In the device herein described, as well as in the known device presently employed, the above-said relays operate depending on the number of the bridges working in the transmisjsion pole at the considered end of the transmission line. Thus, during the operating of one bridge the contacts 1 1-13 are open and the current flowing through the winding 5 from the auxiliary voltage source 9 is minimum, during the operation of four bridges all contacts 11-13 are closed and the current through the winding 5 is maximum. The values of voltages to be applied on the winding of the relay 5 are selected in each case providing for such a relationship between the ampere turns of both windings in which the relay 1 under normal operating conditions of the transmission line does not operate. Thus, the setting for operation of the device by voltage are determined by the values of the resistor 10 and are varied depending on the number of the closed bridges.

On disconnecting one or several bridges on the opposite substation, the voltage of the transmission pole on the given substation in response to the action of the controlling means is lowered, and the current flowing through the bucking winding 2 of the relay 1 is appropriately cut down. The current flowing through the working winding 5 of the relay 1 and depending on the number of the operating bridges retains its former preemergency value exceeding the value of the current flowing through the bucking winding 2. As a result, the relay 1 operates and through the contact 22 triggers the time relay 24 which begins to count the time delay (t,) for disconnecting the first bridge. After closing the contact 26, depending on the position of the switch 30, one of the relays 34-37 operates, thus disconnecting the bridge corresponding to the given position of the switch. For example, when the switch is in the position I, the relay 34 operates through a corresponding contact of the group 31 and switches on the shunting apparatus 14 of the bridge 18.

After switching on the shunting apparatus, its blocking con- 6 5 the working winding of the relay 1 is lowered. If this lowering of the current corresponds to reduction of the current flowing through the bucking winding 2, the relay 1 returns to the initial position, and this corresponds to the same number of operating bridges at both ends of the transmission line.

closed and the time relay 24, while continuing the time counting, closes the circuit of the other time relay 25 through the 7 contact 27. This relay after a time delay 1 required for disconnection of the next bridge, closes the contact 28. As a result, the relay 35 operates through the circuit 1 of the group I If this does not occur, the contact 22 of the relay 1 remains 32 of the switch 30 and switches on the shunting apparatus of the bridge 19. If after the disconnection of the second bridge, the relay 1 is still energized, the contact 29 of the relay is closed after a time delay t and the relay 36 operates through the circuit 1 of the group 33 of the switch 30. The relay 36 switches on the shunting apparatus 16 of the bridge 21. The disconnection of the fourth bridge of the transmission linein case of failure of all the four bridges on the other substation is not carried out as in the case of complete disconnection of the transmission line, other protecting devices of the transmission line are put into operation. Thus the operation of the device results either in the matching of the number of bridges of the transmission pole of both substations, or, when all the bridges are disconnected, in a total disconnection of a given pole. The matching of the number of bridges makes it possible to avoid long operation of the bridge valves of the sound end of the transmission pole at large ignition angles.

The above-mentioned order of disconnection of the bridges corresponds to the position of, the switch and is represented by the left upper column in the time diagram of operation of the device given below.

In other cases the transfer of the time delays is effected in a similar way; the operation of the device in these cases is shown in the corresponding columns of the time diagram.

The contacts 26, 28 and 29 of the time relays 24, 25 are sliding, the time of the closed condition of these contacts is selected sufficient for triggering the circuit to disconnect the bridges but shorter than the time required for switching on he shunting apparatus of the bridges. This is necessary for preventing a false operation of the device, for example, for disconnection with the time t in the first of the abovedescribed cases, of not only the bridge 18 but also the bridge 19 as the relays 1,24,25 can principally be reset to the initial position only after the operation of the shunting apparatus. Therefore, if the contact, immediately after the operation of the apparatus 14 and relay 42, through the closed contact 50 there could be sent a false signal for operation of the relay and for closing the bridge 19, and this is inadmissible.

We claim:

1. A device for matching the number of operating bridges on converting substations of a direct-current transmission line comprising; a comparator for comparing the voltage of the Bridges under operation III At the other positions of the switch with a lower time delays, the bridges corresponding to-these positions are disconnected, the succession of disconnection of the remaining bridges being determined, as mentioned above, by the circuit of connection of the switch with the actuating relays 34-37. For example, in the position Ill after the time delay I the relay 36 is energized through the contacts 26 and the circuit III of the group 31 of the switch 30. The relay 36 operates and switches off the bridge 20, thereafter, energized through the contact 28 and circuit 111 of the group 32 is the relay 34 wEiEiiTWiieB operated, switched ofi the bridge 18, then through the contact 29 and the circuit HI of the group 33 there is operated the relay 35 for switching off the bridge 19. In all cases, just after the selected bridge there is disconnected a bridge nearest to earth, then the bridge more remote from earth as compared to the first bridge.

In the considered embodiment of the device the succession of disconnection of the bridges in a complete circuit is represented by the left column of the diagram. It is possible to employ another succession of disconnection of the bridges after the first, for example, by the principle of increasing the ordinal numbers (taking into account the numbering of the bridges from earth), etc.

If the transmission pole includes a lesser number of bridges, for example, three bridges 19-21, the shunting apparatus 14 of the bridge 18 is switching on, its blocking contact 46 is closed and the relay 42 is energized.

As a result, the contact 50 of the relay 42 is also closed and this, when associated with the position 1 of the switch 30, causes the operation of the device through the contacts 26 (t and 50 of the relay acting for disconnection of the bridge 19, i.e. following the selected bridge according to a predetermined succession of operation of the device.

transmission pole relative to earth with a voltage from an auxiliary source depending on the number of operating bridges of the transmission pole, a unit for disconnecting the bridges connected to the comparator, elements included in said unit having different time delays, said elements being triggered from said comparator and determining the disconnected time of the bridges, shunting means for said bridges, actuating elements for switching on the bridge shunting means, and a switch for selectively disconnecting successive ones of said bridges, said switch having a number of switch positions corresponding to the number of the bridges of the transmission line pole in each sub-station, and said switch having a plurality of circuits divided into groups each having a number of circuits corresponding to the number of the switch positions, the circuits on one side of each said group being interconnected and correspondingly connected to said elements having said different time delays, and the circuits on the other side of each said group being connected to said actuating elements.

2. A device as claimed in claim 1, including commutating elements inserted between the circuits to said actuating elements, each said commutating element being closed in the switched-on position of a corresponding shunting means so as to effect a switching-over of said time delay elements and prepare said device for a successive operation, said time delay elements being adapted to effect the shunting of disconnected ones of said bridges, and said switching-over of these time delay elements effecting the shunting of subsequent ones of bridges, wherein said last-mentioned bridges are adapted to be (Ec'onnected during successive operations of said device in accordance with the remaining portion of a prescribed bridge shunting sequence in dependence upon the switch position. 

1. A device for matching the number of operating bridges on converting substations of a direct-current transmission line comprising; a comparator for comparing the voltage of the transmission pole relative to earth with a voltage from an auxiliary source depending on the number of operating bridges of the transmission pole, a unit for disconnecting the bridges connected to the comparator, elements included in said unit having different time delays, said elements being triggered from said comparator and determining the disconnected time of the bridges, shunting means for said bridges, actuating elements for switching on the bRidge shunting means, and a switch for selectively disconnecting successive ones of said bridges, said switch having a number of switch positions corresponding to the number of the bridges of the transmission line pole in each substation, and said switch having a plurality of circuits divided into groups each having a number of circuits corresponding to the number of the switch positions, the circuits on one side of each said group being interconnected and correspondingly connected to said elements having said different time delays, and the circuits on the other side of each said group being connected to said actuating elements.
 2. A device as claimed in claim 1, including commutating elements inserted between the circuits to said actuating elements, each said commutating element being closed in the switched-on position of a corresponding shunting means so as to effect a switching-over of said time delay elements and prepare said device for a successive operation, said time delay elements being adapted to effect the shunting of disconnected ones of said bridges, and said switching-over of these time delay elements effecting the shunting of subsequent ones of bridges, wherein said last-mentioned bridges are adapted to be disconnected during successive operations of said device in accordance with the remaining portion of a prescribed bridge shunting sequence in dependence upon the switch position. 